1. Field
The disclosed embodiments relate to a substrate transport apparatus and, more particularly, to substrate transport apparatus with multiple movable arms.
2. Brief Description of Related Developments
Conventional non-coaxial side-by-side dual scara arms are offered for sale by several companies; the UTW and UTV series of robots by MECS Korea, Inc., the RR series of robots by Rorze Automation, Inc. and the LTHR, STHR and SPR series of robots by JEL Corp. An example of a side-by-side dual arm scara transfer device can be found in U.S. Pat. No. 5,765,444.
An exemplary configuration of a conventional non-coaxial side-by-side dual arm robot is shown in FIGS. 1 and 1A. The robot is built around a pivoting hub, which carries two scara arms or linkages. The left linkage has an upper arm, a forearm and an end effector coupled in series through revolute joints. A belt and pulley arrangement is used to constrain the motion of the left arm so that rotation of the upper arm with respect to the hub produces rotation of the forearm in the opposite direction (e.g. clockwise upper arm rotation causes counterclockwise forearm rotation). Another belt and pulley arrangement is used to maintain radial orientation of the end effector. The right linkage may be a mirror image of the left arm. The end effectors of the left and right arms move in different horizontal planes to allow for unrestricted motion of the two linkages of the robot. As can be seen in FIGS. 1B-1D, by rotating the left and right upper arms the respective linkages can be extended independently in a common radial direction with respect to the pivot point of the hub.
In the conventional side-by-side robots as shown in FIGS. 1A-D, the robot arms or linkages are actuated by a complex arrangement of three motors, which for example may be configured in a coaxial manner, coupled to the robot through hollow shafts. Typically the outermost shaft is coupled directly to the hub while the two inner shafts are coupled to the upper arms of the left and right linkages through independent belt and pulley arrangements. As may be realized, the larger the number of motors employed for effecting movement of the robot arm, the greater the burden on the control system controlling robot motion. Also, the larger the number of motors employed increases the potential for motor failure as well as the cost of the robot.
It would be advantageous to have a robot manipulator with independently movable arms with reduced complexity and improved reliability and cleanliness of the robotic system.